/*&*/object1="Sun"/*&*/ /*&*/distance1="93 million miles (8.3 lightminutes)"/*&*/ /*&*/blackhole1="No"/*&*/ /*&*/modulebrief1="The Sun is the nearest star, and the center of our solar system. It is medium-size, as stars go, and about halfway through it's 10 billion year lifespan."/*&*/ /*&*/maintext1="Our solar system consists of the Sun and everything that orbits around it. The Sun is at the center and contains 99.9 percent of the mass. It is the closest star to Earth (the next nearest star, Proxima Centauri, is 270,000 times further away). A fairly typical medium-sized star, the Sun is 330,000 times heavier than the Earth, and has 110 times its size.

Stars do not have a solid surface, but consist entirely of hot gas. Like all stars, the Sun was born when a gas cloud contracted and became so hot that atomic nuclei began fusing together. In the Sun, nuclear fusion occurs in the core at 27 million degrees Fahrenheit. The core contains 60 percent of the solar mass, but occupies only 2 percent of its volume. The fusion of hydrogen into helium has already sustained the enormous energy output of the Sun for the past 4.6 billion years. After another 5 billion years it will run out of nuclear fuel and will ultimately fade to obscurity. Stars like our Sun do not become black holes when they die.

The Sun is the only star that can be observed in detail. The visible light image shows the outer layers that shine at 9,900 degrees Fahrenheit. The radio image highlights somewhat cooler regions in these layers, known as sunspots. These spots come and go regularly every 11 years. The X-ray image shows violent magnetic activity on the Sun. It also shows the gaseous envelope known as the corona, which glows in X-rays at 4 million degrees Fahrenheit."/*&*/ /*&*/image1="sun"/*&*/ /*&*/caption1_visible="The Sun as it appears to the eye (wearing protective eye wear!). Two black sunspots can be seen at the center."/*&*/ /*&*/caption1_radio="Sun spots around the solar equator are thousands of miles across. They are sites of intense radio wave emission (colored red)."/*&*/ /*&*/caption1_xray="The tenuous gas of the corona around the Sun reveals itself in X-rays. Sun spots on the solar disk emit X-rays as well."/*&*/ /*&*/link_url1_1="http://www.nineplanets.org/sol.html"/*&*/ /*&*/link_url1_2="http://sunearthday.nasa.gov/"/*&*/ /*&*/link_url1_3="http://www.sunspot.noao.edu/"/*&*/ /*&*/link_url1_4="http://sohowww.nascom.nasa.gov/"/*&*/ /*&*/link_displayed1_1="More facts about the Sun"/*&*/ /*&*/link_displayed1_2="Sun Earth Day"/*&*/ /*&*/link_displayed1_3="US National Solar Observatory"/*&*/ /*&*/link_displayed1_4="SOHO satellite"/*&*/ /*&*/object2="Moon"/*&*/ /*&*/distance2="240,000 miles (1.3 lightseconds)"/*&*/ /*&*/blackhole2="No"/*&*/ /*&*/modulebrief2="The Moon is Earth's companion. It orbits around us once every month, always showing the same face but with changing phases. "/*&*/ /*&*/maintext2="The Moon is the companion of planet Earth. It is the only body in the solar system, besides Earth, that has been visited by humans (for the first time by the Apollo 11 mission in 1969). One-fourth the size of Earth, the moon is made of low-density mantle rock and so is 81 times less massive than the Earth. Orbiting the Earth, it completes one revolution every month. During its revolution around the Earth, the Moon also completes one revolution around its axis. So it always keeps the same side facing towards us.

We see the Moon because it reflects radiation from the Sun. As it rotates around the Earth, it appears to us in different phases: new, crescent, first quarter, gibbous, full, waning gibbous, last quarter, waning crescent, and (again) new. The visible light image of the Moon shows many surface features, including meteorite impact craters. The moon has no atmosphere or water and such craters do not erode away as quickly as on Earth. The X-ray image shows less surface detail and was obtained at a slightly different Moon phase. The radio image is dominated by the Moon's own heat glow and therefore shows the full Moon circle. But the phase is still evident, because the illuminated side is warmer than the unilluminated side.

Moons, which orbit planets, are very common in the solar system. Several planets have more than a dozen. They are all very different from each other and from our own Moon. The solar system also contains objects smaller than moons, such as asteroids, meteoroids and comets."/*&*/ /*&*/image2="moon"/*&*/ /*&*/caption2_visible="Many impact craters can be seen on the Moon's surface. The darker areas on the left are lower lying plains."/*&*/ /*&*/caption2_radio="The red color indicates that the light part of the Moon emits more radio waves than the dark part. This is due to heating by the Sun."/*&*/ /*&*/caption2_xray="The phase of the Moon can also be seen in X-rays, because X-rays from the Sun are reflected by the Moon."/*&*/ /*&*/link_url2_1="http://www.nineplanets.org/luna.html"/*&*/ /*&*/link_url2_2="http://www.fourmilab.ch/earthview/vplanet.html"/*&*/ /*&*/link_url2_3="http://nssdc.gsfc.nasa.gov/planetary/lunar/apollo_11_30th.html"/*&*/ /*&*/link_url2_4="http://www.nasa.gov/externalflash/Vision/main.html"/*&*/ /*&*/link_displayed2_1="More facts about the Moon"/*&*/ /*&*/link_displayed2_2="Viewing the Moon"/*&*/ /*&*/link_displayed2_3="The Apollo 11 mission"/*&*/ /*&*/link_displayed2_4="NASA human space exploration"/*&*/ /*&*/object3="Saturn (Planet)"/*&*/ /*&*/distance3="890 million miles (1.3 lighthours)"/*&*/ /*&*/blackhole3="No"/*&*/ /*&*/modulebrief3="Sixth planet from the Sun, Saturn is the second largest planet after Jupiter. It is encircled by a beautiful system of very thin rings, made up of icy debris that orbits around the equator."/*&*/ /*&*/maintext3="Saturn is the second largest (after Jupiter) of our solar system's planets. One of the giant Jovian Planets that roam the outer solar system, it is 95 times heavier than the Earth, and nearly ten times its size. It takes 29.5 years to orbit the Sun.

Saturn is encircled by a beautiful system of very thin rings, made up of icy debris that orbits at the equator. The visible light image shows the rings, as well as bands of clouds in Saturn's atmosphere. The observed light is sunlight that gets reflected back to us by the planet. By contrast, the radio image is dominated by Saturn's own heat glow. In X-rays it is possible to detect the planet, but little detail is evident.

Many stars in the Universe host a system of planets. Astronomers have detected Jovian planets around many nearby stars. However, the detection methods have been indirect and images of these planets do not exist. Terrestrial planets have thus far proven too small and faint to detect around other stars. In our solar system, Mercury, Venus, Earth and Mars are the rocky Terrestrial Planets and orbit closest to the Sun. Further away, the Jovian Planets (Jupiter, Saturn, Uranus and Neptune) are mostly made of gas. They have no solid surface. All planets have been explored with unmanned spacecraft. Voyager 2 visited all four Jovian planets, taking 12 years after its launch in 1977 to reach Neptune. Pluto was long considered the ninth planet but was recently reclassified as a ''dwarf planet'', a class of objects in the outer solar system made mostly of ices."/*&*/ /*&*/image3="saturn"/*&*/ /*&*/caption3_visible="Visible light from Saturn and its rings is reflected Sunlight. The gap between the rings is called the Cassini division."/*&*/ /*&*/caption3_radio="The cold (colored blue) rings and the warmer (color red) surface emit radio waves produced by Saturn itself."/*&*/ /*&*/caption3_xray="90 Megawatts of X-ray power (colored white) comes from Saturn's equator. These are mostly reflected X-rays from the Sun."/*&*/ /*&*/link_url3_1="http://www.nineplanets.org/saturn.html"/*&*/ /*&*/link_url3_2="http://soc.jpl.nasa.gov/viewing.cfm"/*&*/ /*&*/link_url3_3="http://saturn.jpl.nasa.gov/home/index.cfm"/*&*/ /*&*/link_url3_4="http://exoplanets.org/exoplanets_pub.html"/*&*/ /*&*/link_displayed3_1="More facts about Saturn"/*&*/ /*&*/link_displayed3_2="Viewing Saturn"/*&*/ /*&*/link_displayed3_3="Cassini-Huygens explorer"/*&*/ /*&*/link_displayed3_4="Planets around other stars"/*&*/ /*&*/object4="Albireo (Binary star)"/*&*/ /*&*/distance4="380 lightyears"/*&*/ /*&*/blackhole4="No"/*&*/ /*&*/modulebrief4="Albireo is a binary system--two stars bound together by their mutual gravitational attraction. The stars in Albireo are not special enough to show up in radio waves or X-rays."/*&*/ /*&*/maintext4="Albireo in the constellation Cygnus (Swan) appears as a single point of light to the naked eye, but a telescope shows it to be a binary star: two stars bound together by their mutual gravitational attraction. The stars take thousands of years to orbit around each other. More than half of all stars live in binary systems. The Sun is somewhat unusual in that it is solitary.

In Albireo one can see both stars -- one star is cool and appears orange, the other hotter and blue. In more typical binaries, the stars are so close together that only one source can be seen. Even so, it is often possible to infer the presence of a companion, as well as the properties of its orbit. This generally involves studying the stellar spectrum (the distribution of its light over many wavelengths, in the same way that a rainbow shows the wavelength distribution of sunlight). Knowing the binary orbit lets us calculate the masses of both stars.

Radio and X-ray images of Albireo show nothing, because normal stars are much brighter in visible light than at other wavelengths. We can make radio and x-ray images of the Sun at all wavelengths because it is so close. But for a more distant star, we usually cannot detect radio waves or X-rays, unless the star is somehow unusual, such as a star in orbit around a black hole. These binaries can be very bright in X-rays."/*&*/ /*&*/image4="alberio"/*&*/ /*&*/caption4_visible="The hot (20,000 degrees Fahrenheit) blue and cooler (8,000 degrees) orange star (a red giant) orbit around each other."/*&*/ /*&*/caption4_radio="The stars in Albireo are too faint in radio waves to be detected."/*&*/ /*&*/caption4_xray="The stars in Albireo are too faint in X-rays to be detected."/*&*/ /*&*/link_url4_1="http://www.astronomical.org/astbook/binary.html"/*&*/ /*&*/link_url4_2="http://instruct1.cit.cornell.edu/courses/astro101/java/binary/binary.htm"/*&*/ /*&*/link_url4_3="http://antwrp.gsfc.nasa.gov/apod/ap970219.html"/*&*/ /*&*/link_url4_4="http://skyandtelescope.com/howto/basics/article_237_1.asp"/*&*/ /*&*/link_displayed4_1="More facts about binary stars"/*&*/ /*&*/link_displayed4_2="Simulate binary star orbits"/*&*/ /*&*/link_displayed4_3="Another famous binary: Mizar"/*&*/ /*&*/link_displayed4_4="Origins of star names"/*&*/ /*&*/object5="Betelgeuse (Red giant)"/*&*/ /*&*/distance5="430 lightyears"/*&*/ /*&*/blackhole5="No"/*&*/ /*&*/modulebrief5="Betelgeuse is a red giant, emitting 16,000 times more visible light than the Sun (but it is too distant to detect in X-rays). All stars become a red giant late in life."/*&*/ /*&*/maintext5="The star Betelgeuse, in the constellation Orion, is 500 times bigger and emits 16,000 times more visible light than the Sun. This is why the star appears so bright on the sky, despite its considerable distance. Betelgeuse is redder than our Sun, which implies that it is cooler. Its outer layers radiate at 5000 degrees Fahrenheit. Because of its color and size, Betelgeuse is called a red giant.

Most stars in the Universe appear to us as points of light. But Betelgeuse is so large that it reveals a disk when observed with the best telescopes. The visible light and radio images show a slightly non-circular appearance. This is probably due to activity in the outer layers of its atmosphere, similar to the Sun's corona. But even this giant star's x-rays are too weak to detect from Earth.

A star becomes a red giant late in its life, when nuclear fusion has transformed all the hydrogen in the core into helium. The resulting increases in size and brightness mark the beginning of the end for the star. Heavy stars turn into red giants more quickly than light stars. Betelgeuse is some 12 times heavier than the Sun. It is already a red giant, despite being only some 7 million years old. By contrast, the Sun will not become a red giant until its age reaches 10 billion years, another 5 billion years from now. Red giants that are at least twice as heavy as Betelgeuse later become black holes after a supernova explosion."/*&*/ /*&*/image5="betelgeuse"/*&*/ /*&*/caption5_visible="Betelgeuse is much brighter than the Sun. But it is also cooler, and therefore appears redder when seen in the night sky."/*&*/ /*&*/caption5_radio="The asymmetric structure of Betelgeuse in radio waves is likely due to activity in the outer atmosphere of the star."/*&*/ /*&*/caption5_xray="Betelgeuse is too faint in X-rays to be detected."/*&*/ /*&*/link_url5_1="http://en.wikipedia.org/wiki/Betelgeuse"/*&*/ /*&*/link_url5_2="http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/04/"/*&*/ /*&*/link_url5_3="http://www.star.le.ac.uk/edu/Stars.shtml"/*&*/ /*&*/link_url5_4="http://observe.arc.nasa.gov/nasa/space/stellardeath/stellardeath_intro.html"/*&*/ /*&*/link_displayed5_1="More facts about Betelgeuse"/*&*/ /*&*/link_displayed5_2="Betelgeuse imaged by Hubble"/*&*/ /*&*/link_displayed5_3="The study of stars"/*&*/ /*&*/link_displayed5_4="Stellar evolution and death"/*&*/ /*&*/object6="NGC 7027 (Planetary nebula)"/*&*/ /*&*/distance6="2,600 lightyears"/*&*/ /*&*/blackhole6="No"/*&*/ /*&*/modulebrief6="This nebula is the glowing gaseous envelope of a dying star that has shed its outer layers. This is the ultimate fate of all stars like our Sun."/*&*/ /*&*/maintext6="This object in the constellation Cygnus (Swan) is number 7027 in the New General Catalog, a famous list of bright gas clouds, star clusters, and galaxies. The name planetary nebulae was given long ago to objects that appeared fuzzy and resembled planets through a small telescope. However, these objects have nothing to do with planets. Instead, they form when a star slowly sheds its outer gas layers towards the end of its life.

The visible light image of NGC 7027 shows the dying star as a dot, surrounded by the gas that it has shed. The radiation from the star causes atoms in the gas to glow in a brilliant display. The radio and X-ray images show different radiation from the same gas. The radio waves reveal the heat glow from relatively cool gas in the cloud, whereas the X-rays are produced only by the very hottest gas regions.

When a star nears the end of its life, it first becomes a red giant. What happens next depends on the mass of the star. Stars that are no more than eight times heavier than the Sun die relatively peacefully, lacking sufficient mass to become a black hole. They shed their outer layers and are visible as planetary nebulae for about 100,000 years. The stellar remnant is about as heavy as the Sun, but the mass is packed in a volume only about the size of the Earth. Because of its high temperature and small size it is called a white dwarf. It has no more nuclear fusion to support its temperature, so it cools slowly and eventually fades into obscurity."/*&*/ /*&*/image6="ngc7027"/*&*/ /*&*/caption6_visible="A dying star (the white dot in the center) has ejected its outer layers. The ejected gas glows in white, pink and red light."/*&*/ /*&*/caption6_radio="Radio waves from glowing gas yield a measurement of the gas temperature (red is warmer; blue is colder)."/*&*/ /*&*/caption6_xray="Regions with hot gas emit X-rays. This gas is distributed rather differently than the cooler gas visible in the radio image."/*&*/ /*&*/link_url6_1="http://www.astro.washington.edu/balick/WFPC2/"/*&*/ /*&*/link_url6_2="http://antwrp.gsfc.nasa.gov/apod/planetary_nebulae.html"/*&*/ /*&*/link_url6_3="http://en.wikipedia.org/wiki/Planetary_nebula"/*&*/ /*&*/link_url6_4="http://en.wikipedia.org/wiki/White_dwarf"/*&*/ /*&*/link_displayed6_1="Hubble images of planetary nebulae"/*&*/ /*&*/link_displayed6_2="Other images of Planetary Nebulae"/*&*/ /*&*/link_displayed6_3="More facts about planetary nebulae"/*&*/ /*&*/link_displayed6_4="More facts about white dwarfs"/*&*/ /*&*/object7="Crab Nebula (Supernova remnant)"/*&*/ /*&*/distance7="6,000 lightyears"/*&*/ /*&*/blackhole7="No"/*&*/ /*&*/modulebrief7="This nebula is the gaseous left-over of a supernova, the explosion that marked the death of a heavy star. The stellar core survived the explosion as a pulsating neutron star (pulsar)."/*&*/ /*&*/encycintro7="TBD"/*&*/ /*&*/maintext7="In the year 1054, ancient astronomers noted the appearance of a bright new star in the constellation Taurus (Bull). It was visible in broad daylight for more than a month before fading from view. This supernova (nova means new) was the explosion that marked the death of a massive star. What we observe in its place today is a supernova remnant, the glowing gaseous remains expelled into space by the exploding star.

The leftover energy from the explosion makes the remnant very bright at all wavelengths. The visible light and radio images are vaguely reminiscent of a Crab and highlight the turbulent filamentary structure of gas. The X-ray image shows a zoom by a factor four of the very central region.

All stars with a birth mass more than eight times that of the Sun die in a spectacular supernova. But if the star wasn't too much heavier than that, the stellar core survives the supernova as a neutron star (it is not massive enough to become a black hole). This is a dense ball of neutral elementary particles. It is somewhat more massive than the Sun, but is squeezed into a space little more than 10 miles across. The Crab supernova produced a neutron star, seen as the dot in the center of the X-ray image. The neutron star spins rapidly and emits a bright beam of radiation from its magnetic poles. Like a cosmic lighthouse, this beams sweeps past the Earth 30 times per second. We observe this as regular pulses and call such a neutron star a pulsar (short for pulsating star)."/*&*/ /*&*/image7="crabnebula"/*&*/ /*&*/caption7_visible="Hot gas (blue) was blown out by a stellar explosion almost 1000 years ago. A web of cooler gas (red) is also visible."/*&*/ /*&*/caption7_radio="Radio waves show a web-like structure. This is caused by shocks that propagate as ripples through the ejected gas."/*&*/ /*&*/caption7_xray="The exploding star has left a pulsar (central dot). Jets of X-ray emitting matter are expelled in opposite directions. "/*&*/ /*&*/link_url7_1="http://en.wikipedia.org/wiki/Supernova"/*&*/ /*&*/link_url7_2="http://antwrp.gsfc.nasa.gov/apod/supernova_remnants.html"/*&*/ /*&*/link_url7_3="http://www.supernovae.net/isn.htm"/*&*/ /*&*/link_url7_4="http://www.windows.ucar.edu/tour/link=/cool_stuff/tourstars_1.html&edu=elem&link_url=/sun/Solar_interior/Nuclear_Reactions/Fusion/Fusion_in_stars/star_life.html"/*&*/ /*&*/link_displayed7_1="More facts about supernovae"/*&*/ /*&*/link_displayed7_2="Images of supernova remnants"/*&*/ /*&*/link_displayed7_3="International Supernova Network"/*&*/ /*&*/link_displayed7_4="The Lives of Stars"/*&*/ /*&*/object8="Cygnus X-1 (X-Ray binary)"/*&*/ /*&*/distance8="8,100 lightyears"/*&*/ /*&*/blackhole8="Yes (stellar-mass)"/*&*/ /*&*/modulebrief8="This binary consists of a star and a black hole orbiting around each other. The black hole pulls gas off the star, which heats up and shines in X-rays as it falls towards the black hole."/*&*/ /*&*/maintext8="This is the brightest X-ray source (indicated as X-1) in the constellation Cygnus (Swan). It consists of a bright blue star and a black hole that orbit around each other. The black hole pulls gas off the surface of this star. This gas heats up and shines in X-rays as it falls towards the black hole.

The X-ray image shows the hot gas around the black hole. The radio image shows that energetic processes accelerate electrons to high speeds. These electrons emit radio waves as they are being expelled in a jet (towards the top right). The visible light image shows a normal bright star at the same position as the X-ray source (the other stars in the image are unrelated and reside in the foreground or background). Analysis of the stellar spectrum reveals that the star revolves around its unseen companion every 5.6 days.

When a star with a birth mass at least 25 times heavier than the Sun dies in a supernova explosion, its core is too massive to withstand its own gravity. It collapses and forms a black hole. We call this a stellar-mass black hole (as opposed to supermassive black holes, which are typically a million times heavier). A stellar-mass black hole is normally invisible to us. But in a binary system, bright X-rays might give away its presence. Cygnus X-1 is an unusual X-ray binary because we can determine the mass of the unseen companion. It's about 10 times more massive than the Sun. In fact, this proves that it must be a black hole. Neutron stars and white dwarfs can also power X-ray binaries, but they cannot be this heavy."/*&*/ /*&*/image8="cygnusX-1"/*&*/ /*&*/caption8_visible="The brightest star in this image is orbiting around a black hole every 5.6 days. The black hole itself cannot be seen."/*&*/ /*&*/caption8_radio="The black hole in Cygnus X-1 ejects a jet of material (towards the upper right) that shines in radio waves."/*&*/ /*&*/caption8_xray="The black hole pulls gas of the star orbiting around it. The gas heats up and emits X-rays (yellow) as it falls into the black hole."/*&*/ /*&*/link_url8_1="http://imagine.gsfc.nasa.gov/docs/science/know_l1/binary_stars.html"/*&*/ /*&*/link_url8_2="http://imagine.gsfc.nasa.gov/YBA/cyg-X1-mass/binary.html"/*&*/ /*&*/link_url8_3="http://chandra.harvard.edu/photo/2003/bhspin/"/*&*/ /*&*/link_url8_4="http://chandra.harvard.edu/photo/constellations/cygnus.html"/*&*/ /*&*/link_displayed8_1="More facts about X-ray binaries"/*&*/ /*&*/link_displayed8_2="The mass of Cygnus X-1"/*&*/ /*&*/link_displayed8_3="The spin of Cygnus X-1"/*&*/ /*&*/link_displayed8_4="The constellation Cygnus (Swan)"/*&*/ /*&*/object9="Andromeda (Spiral galaxy)"/*&*/ /*&*/distance9="2.5 million lightyears"/*&*/ /*&*/blackhole9="Yes (supermassive)"/*&*/ /*&*/modulebrief9="A nearby spiral galaxy with a black hole in its center. The quiescent black hole doesn't show up as a strong source of energetic activity in radio and X-ray images."/*&*/ /*&*/maintext9="The Andromeda galaxy, named after the constellation in which it resides, is the nearest galaxy to us that is similar in size to our own Milky Way galaxy. Its main body has the shape of a flat circular disk, which appears elongated to us because we view it from the side. The central region of the galaxy has a more rounded shape and is called, cleverly, the bulge.

The visible light image shows that the distribution of stars resembles a spiral pattern. Andromeda therefore belongs to the class of spiral galaxies. Some of the stars reside in binary systems that emit X-rays. These binaries show up as points in the X-ray image. The galaxy disk also contains cold dust and hydrogen gas. The dust obscures some of the starlight and produces the dark bands in the visible light image. The cold hydrogen gas glows in radio waves, shown in the radio image.

We know from measurements of the velocities of stars that there is a supermassive black hole in the galaxy center, 30 million times heavier than the Sun. The black hole is called quiescent because it does not show up in radio and X-ray images as a source of particularly energetic activity. This contrasts with the active black holes in some other galaxies, which are avidly consuming material and producing bright radio waves and X-rays. Most large galaxies have a supermassive black hole in their center, and most of them are quiescent. Galaxies with bigger bulges have heavier black holes."/*&*/ /*&*/image9="andromeda"/*&*/ /*&*/caption9_visible="A central bulge of stars is surrounded by a disk with obscuring dust clouds (dark strands) and young stars (blue light)."/*&*/ /*&*/caption9_radio="Cold hydrogen gas in the Andromeda disk emits radio waves (colored yellow). There is less gas near the galaxy center."/*&*/ /*&*/caption9_xray="Most stars in a galaxy cannot be detected in X-rays. The dots in the image are due to a small number of X-ray binary systems."/*&*/ /*&*/link_url9_1="http://www.seds.org/messier/m/m031.html"/*&*/ /*&*/link_url9_2="http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/15/"/*&*/ /*&*/link_url9_3="http://www.seds.org/messier/more/local.html"/*&*/ /*&*/link_url9_4="http://www.anzwers.org/free/universe/localgr.html"/*&*/ /*&*/link_displayed9_1="More facts about Andromeda"/*&*/ /*&*/link_displayed9_2="Stars around Andromeda"/*&*/ /*&*/link_displayed9_3="The Local Group of Galaxies"/*&*/ /*&*/link_displayed9_4="An atlas of the Universe"/*&*/ /*&*/object10="Milky Way Center"/*&*/ /*&*/distance10="28,000 lightyears"/*&*/ /*&*/blackhole10="Yes (supermassive)"/*&*/ /*&*/modulebrief10="This is the heart of the galaxy (the luminous band in the sky) that hosts our Earth and Sun. The black hole there reveals itself through energetic emission seen in radio and X-ray images."/*&*/ /*&*/maintext10="In the center of the galaxy in which we live, seen in the constellation Sagittarius (Archer), there lies a black hole. We can see its imprint in the radio and the X-ray image. Material that falls down to the black hole heats up. This results in energetic processes that generate radio waves and X-rays that we can observe. By contrast, in visible light dust particles in our galaxy obscure our view. So we cannot directly see the center of our galaxy; the stars seen in the visible light image are all in the foreground.

Like all galaxies, our galaxy contains billions of stars. Most of them live in a flat disk-shaped structure. Our Sun lies about two-thirds out from the center. Looking along the plane of the disk we see many stars, but looking perpendicular to it we see very few. Our galaxy therefore appears to us as the luminous band across the sky that our ancestors named the Milky Way.

The Sun moves around the center of our galaxy in the same way that the Earth moves around the Sun -- but it takes 250 million years to complete one orbit. The Sun never gets close to the black hole in the center of the Milky Way, but some other stars do. Astronomers have used observations in infrared light to measure the speeds of such stars. Infrared light has longer wavelengths than visible light, which allows it to penetrate the dust in our Milky Way. It can be calculated from the measured speeds that the black hole in the center of our Milky Way is three million times heavier than the Sun. Such black holes are called, not surprisingly, supermassive."/*&*/ /*&*/image10="milkyway"/*&*/ /*&*/caption10_visible="A view towards the center of our Milky Way shows only nearby foreground stars. Dust clouds obscure the actual center from view."/*&*/ /*&*/caption10_radio="The radio waves are most intense (colored red) from gas close to the black hole. Magnetic fields create structures in the gas."/*&*/ /*&*/caption10_xray="Lobes of hot gas (red) surround the Milky Way center. The black hole is located inside the white region of intense X-ray emission."/*&*/ /*&*/link_url10_1="http://curious.astro.cornell.edu/milkyway.php"/*&*/ /*&*/link_url10_2="http://cassfos02.ucsd.edu/public/tutorial/MW.html"/*&*/ /*&*/link_url10_3="http://www.eso.org/outreach/press-rel/pr-2002/pr-17-02.html"/*&*/ /*&*/link_url10_4="http://chandra.harvard.edu/photo/2002/gcenter/index.html"/*&*/ /*&*/link_displayed10_1="Simple questions about the Milky Way"/*&*/ /*&*/link_displayed10_2="More facts about the Milky Way"/*&*/ /*&*/link_displayed10_3="Stars orbiting the black hole"/*&*/ /*&*/link_displayed10_4="The Milky Way imaged by Chandra"/*&*/ /*&*/object11="M33 (Extragalactic binaries)"/*&*/ /*&*/distance11="2.1 million lightyears"/*&*/ /*&*/blackhole11="Yes (stellar-mass)"/*&*/ /*&*/modulebrief11="This nearby spiral galaxy has many X-ray binaries, some of which are powered by black holes. However, most of the millions of stellar-mass black holes in a galaxy are invisible to us."/*&*/ /*&*/maintext11="This galaxy is number 33 in a famous 18th century catalog of extended objects compiled by Messier, a French comet-hunter. It is also called the Triangulum (Triangle) galaxy, after the constellation in which it resides. It is the third largest nearby galaxy, after Andromeda and the Milky Way. The visible light image shows that the stars are distributed in a spiral pattern. The radio image shows glowing cold hydrogen gas between the stars.

During the life of a galaxy, billions of stars are born. Most of the heaviest stars have already died and have become white dwarfs, neutron stars, or stellar-mass black holes (depending on their birth mass). In isolation, such compact stellar remnants generally cannot be detected. But a very small fraction resides in a binary system and produces bright X-rays by pulling in gas from a normal companion star. The X-ray image of M33 shows that we can detect such binaries also outside of our own galaxy (extragalactic). Each dot in the image is an X-ray binary. It is difficult to tell what type of compact object powers each binary, but we can be certain that some are powered by black holes. Every galaxy has millions of stellar-mass black holes, although most of them are invisible to us.

Unlike many other large galaxies, such as the Milky Way and Andromeda, M33 does not have a supermassive black hole in its center. Astronomers don't yet fully understood why some galaxies grow supermassive black holes in their centers while others don't."/*&*/ /*&*/image11="m33"/*&*/ /*&*/caption11_visible="M33 has spiral structure that is traced by blue young stars. Unlike the Andromeda galaxy, there is no central bulge."/*&*/ /*&*/caption11_radio="Cold gas (colored red) emits mostly in radio waves and is concentrated in the spiral arms of the galaxy."/*&*/ /*&*/caption11_xray="Each dot is a binary system that shines in X-rays. A compact object, in some cases a black hole, pulls matter of a normal star."/*&*/ /*&*/link_url11_1="http://www.seds.org/messier/m/m033.html"/*&*/ /*&*/link_url11_2="http://coolcosmos.ipac.caltech.edu/cosmic_classroom/multiwavelength_astronomy/multiwavelength_museum/m33.html"/*&*/ /*&*/link_url11_3="http://cas.sdss.org/dr3/en/proj/advanced/galaxies/tuningfork.asp"/*&*/ /*&*/link_url11_4="http://www.seds.org/messier"/*&*/ /*&*/link_displayed11_1="More facts about M33"/*&*/ /*&*/link_displayed11_2="Multiwavelength images of M33"/*&*/ /*&*/link_displayed11_3="Classification of galaxy shapes"/*&*/ /*&*/link_displayed11_4="The Messier Catalog"/*&*/ /*&*/object12="Cygnus A (Elliptical galaxy)"/*&*/ /*&*/distance12="730 million lightyears"/*&*/ /*&*/blackhole12="Yes (supermassive)"/*&*/ /*&*/modulebrief12="This distant galaxy has an active black hole in its center that consumes large amounts of material. The energy thus produced makes it the second brightest radio source in the sky."/*&*/ /*&*/maintext12="This galaxy is the brightest radio source (as indicated by the letter A) in the constellation Cygnus (Swan). The supermassive black hole in its center is a billion times heavier than the Sun. Although the galaxy is relatively distant (300 times further away than the Andromeda galaxy), it appears to us as the second brightest radio source in the entire sky. This is because the black hole generates tremendous energy as it consumes large amounts of material. Nearby electrons are accelerated in this process, emitting strong radio waves as they spiral outward in magnetic fields.

Cygnus A is an elliptical galaxy, with billions of stars in its featureless oval. The dark streaks in the visible image are bands of dust blocking the starlight. In the radio image, thin jets of material lead from the black hole to two giant lobes on either side of the galaxy. These lobes extend ten times further from the galaxy center than the stars in the visible image (the images are not shown to the same scale). The galaxy is enclosed in a cocoon of hot gas that glows in X-rays. Radio and X-ray hot spots are visible where the jets collide with the surrounding gas.

Most large galaxies have a supermassive black hole in their center. But only in a few percent of galaxies does the black hole consume enough material to generate spectacular activity. Cygnus A is one such example. Both elliptical and spiral galaxies can be active in X-rays, but very bright radio emissions are generally seen only in elliptical galaxies."/*&*/ /*&*/image12="cygnusA"/*&*/ /*&*/caption12_visible="The combined light from billions of stars gives this galaxy an elliptical shape. Darker wisps near the center are dust clouds."/*&*/ /*&*/caption12_radio="Two thin jets carry material from the black hole out of the galaxy. There the particles disperse over lobes that emit radio waves."/*&*/ /*&*/caption12_xray="Hot gas surrounds the galaxy. It is particularly bright in X-rays (two yellow spots) where the jets run into the gas."/*&*/ /*&*/link_url12_1="http://chandra.harvard.edu/photo/2000/0216/index.html"/*&*/ /*&*/link_url12_2="http://www.nrao.edu/imagegallery/php/level3.php?id=110"/*&*/ /*&*/link_url12_3="http://imagine.gsfc.nasa.gov/docs/science/know_l1/active_galaxies.html"/*&*/ /*&*/link_url12_4="http://www.cv.nrao.edu/~abridle/images.htm"/*&*/ /*&*/link_displayed12_1="Cygnus A imaged by Chandra"/*&*/ /*&*/link_displayed12_2="Cygnus A imaged by the VLA"/*&*/ /*&*/link_displayed12_3="More facts about active galaxies"/*&*/ /*&*/link_displayed12_4="Radio images of active galaxies"/*&*/ /*&*/object13="3C273 (Quasar)"/*&*/ /*&*/distance13="2.5 billion lightyears"/*&*/ /*&*/blackhole13="Yes (supermassive)"/*&*/ /*&*/modulebrief13="This quasar is an active black hole consuming large amounts of material in the center of a distant galaxy. The energy produced is so large that it outshines the rest of the galaxy."/*&*/ /*&*/maintext13="This quasar in the constellation Virgo greatly puzzled astronomers when it was discovered, until they realized in the 1960s that it is a distant galaxy with a supermassive black hole in its center. The black hole is a billion times heavier than the Sun. It generates so much energy by consuming material that it outshines the rest of the galaxy a hundredfold. The name 'quasar' stands for quasi-stellar object, since that was astronomer's best description of this object at first. The name 3C273 identifies it as number 273 in the third Cambridge catalog of radio sources.

The visible light image of 3C273 shows bright light from near the black hole, as well as a wiggly jet. The latter consists of electrons propelled outwards by the energy generated near the black hole. The jet is seen even more clearly in the radio and X-ray images. 3C273 is a prototypical quasar, but it does have some unusual features. It shines brightly in radio waves, which is true for only ten percent of all quasars. And although such quasars often have jets, they rarely reveal themselves in visible light.

3C273 is one thousand times further away than the Andromeda galaxy, but most quasars are even further away. Their light has traveled so long to get to us that we see them when they were still young. Most galaxies that are now old, with a quiescent supermassive black hole in their center, probably passed through a phase of quasar activity in their youth."/*&*/ /*&*/image13="quasar"/*&*/ /*&*/caption13_visible="Light from close to the supermassive black hole outshines all the stars in the galaxy. The spikes are camera artifacts."/*&*/ /*&*/caption13_radio="Particles get propelled in a jet from near the black hole (at white dot). The jet shines in visible light, radio waves and X-rays."/*&*/ /*&*/caption13_xray="The region just outside the black hole event horizon shines very bright in X-rays (colored yellow). The jet is seen as well."/*&*/ /*&*/link_url13_1="http://chandra.harvard.edu/photo/2000/0131/index.html"/*&*/ /*&*/link_url13_2="http://hubblesite.org/newscenter/newsdesk/archive/releases/2003/03/image/b"/*&*/ /*&*/link_url13_3="http://en.wikipedia.org/wiki/Superluminal_motion"/*&*/ /*&*/link_url13_4="http://antwrp.gsfc.nasa.gov/apod/ap981211.html"/*&*/ /*&*/link_displayed13_1="3C273 imaged by Chandra"/*&*/ /*&*/link_displayed13_2="3C273 imaged by Hubble"/*&*/ /*&*/link_displayed13_3="Superluminal motion in jets"/*&*/ /*&*/link_displayed13_4="The most distant quasars"/*&*/ /*&*/observatoryName14="Visible Light"/*&*/ /*&*/maintext14="When our eyes look at the heavens we see the visible light from stars and other objects in the Universe. Thousands of years ago astronomers in Greece and other ancient cultures already built a detailed understanding of the night sky. Many names and concepts then developed are still in use today. However, our human eyes are actually not very sensitive and modern astronomers use sophisticated telescopes to study the Universe.

The first telescope, invented 400 years ago, used an arrangement of lenses and was small enough to hold by hand. Modern telescopes are much larger, so that more light can be caught and fainter objects can be seen. Curved mirrors are used to focus the light and record it on sophisticated electronic equipment. The 5 meter (200 inch) Hale telescope on California's Palomar Mountain, completed in 1948, was the largest telescope for several decades. This honor is now held by the two Keck telescopes on Mauna Kea in Hawaii, each with a mirror diameter of 10 meters.

To minimize image blurring due to the Earth's atmosphere, telescopes are usually built on high mountains. Mirror deformation technologies now also exist to correct for atmospheric blurring. But even better results are achieved with a telescope in orbit above the Earth atmosphere, such as the Hubble Space Telescope. It has a 2.4 meter diameter mirror in a satellite the size of a school bus. It has produced some of the sharpest and most stunning images ever obtained, has found supermassive black holes in many galaxies, and continues to revolutionize our understanding of the Universe."/*&*/ /*&*/image14="visible"/*&*/ /*&*/caption14_visible="The Hubble Space Telescope flies around the Earth and provides stunning images from high above the atmosphere."/*&*/ /*&*/caption14_radio="The Palomar Hale 5 meter telescope inside its dome (inset on left). Grasp the scale by looking at the ladder below the telescope."/*&*/ /*&*/caption14_xray="The 10 meter Keck telescopes on Hawaii's Mauna Kea mountain. Grasp the scale by looking at the cars in front of the building."/*&*/ /*&*/link_url14_1="http://en.wikipedia.org/wiki/Telescope"/*&*/ /*&*/link_url14_2="http://www.astro.caltech.edu/observatories"/*&*/ /*&*/link_url14_3="http://hubblesite.org/"/*&*/ /*&*/link_url14_4="http://skyandtelescope.com/howto/basics/article_260_1.asp"/*&*/ /*&*/link_displayed14_1="More facts about telescopes"/*&*/ /*&*/link_displayed14_2="Palomar | Keck Observatories"/*&*/ /*&*/link_displayed14_3="Hubble Space Telescope"/*&*/ /*&*/link_displayed14_4="How to make stargazing your hobby"/*&*/ /*&*/observatoryName15="X-rays"/*&*/ /*&*/maintext15="Visible light is the type of 'electromagnetic radiation' to which our eyes are sensitive. But there are many other types of such radiation, all characterized by different wavelengths. If the wavelength is much shorter than that of visible light we speak about X-rays. We encounter X-rays often in our daily lives, for example at the hospital or during security screening.

X-rays have much higher energy than visible light and cannot pass through the Earth atmosphere. So one must launch a special kind of telescope above the atmosphere to see X-rays from astronomical objects. The first X-ray telescopes in the 1960s led to many important discoveries (as recognized by the 2002 Nobel Prize in Physics). X-ray astronomy is now routinely used to provide insight into some of the most energetic processes in the Universe, including the swallowing of matter by black holes. The most powerful X-ray telescopes that currently orbit the Earth are the Chandra X-ray Observatory and XMM Newton telescope.

Electromagnetic radiation with wavelengths between those of X-rays and visible light is called ultraviolet light. We encounter ultraviolet light in our daily lives for example in fluorescent lamps. Ultraviolet telescopes allow astronomers to study things such as the composition of the gas that exists between stars. The Far Ultraviolet Spectroscopic Explorer (FUSE) and the Galaxy Evolution Explorer (GALEX) satellites are two of the most powerful ultraviolet telescopes. Radiation that has even higher energy than X-rays is called gamma-rays, and can also be detected from astronomical objects."/*&*/ /*&*/image15="xray"/*&*/ /*&*/caption15_visible="Artist impression of the Chandra X-ray Observatory. It can take sharper X-ray images than any other telescope."/*&*/ /*&*/caption15_radio="Artist impression of the XMM Newton X-ray Observatory. It can detect fainter X-ray signals then any other telescope."/*&*/ /*&*/caption15_xray="Artist impression of the GALEX satellite, which can make images of the ultraviolet light from astronomical objects."/*&*/ /*&*/link_url15_1="http://imagine.gsfc.nasa.gov/docs/introduction/xray_information.html"/*&*/ /*&*/link_url15_2="http://chandra.harvard.edu/"/*&*/ /*&*/link_url15_3="http://xmm.sonoma.edu/index.html"/*&*/ /*&*/link_url15_4="http://fuse.pha.jhu.edu/outreach/"/*&*/ /*&*/link_displayed15_1="More facts about X-ray astronomy"/*&*/ /*&*/link_displayed15_2="The Chandra X-ray Observatory"/*&*/ /*&*/link_displayed15_3="The XMM-Newton X-ray telescope"/*&*/ /*&*/link_displayed15_4="The Far Ultraviolet Spectroscopic Explorer"/*&*/ /*&*/observatoryName16="Radio Waves"/*&*/ /*&*/maintext16="Visible light is the type of 'electromagnetic radiation' to which our eyes are sensitive. But there are many other types of such radiation, all characterized by different wavelengths. If the wavelength is much larger than that of visible light we speak about radio waves. We encounter radio waves often in our daily lives, for example in radios and cell phones.

In the mid 1900s it was discovered that many objects in the Universe shine in radio waves. This led to the development of radio telescopes, which are special antennas for detecting and imaging the radio signals from astronomical objects. Radio telescopes have yielded new insights into many aspects of the Universe, including black holes and cool gas. The largest single-dish radio telescope is the Arecibo Telescope in Puerto Rico. With a radio interferometer astronomers create very sharp images by combining the signals from many individual radio dishes spread over a large area. The Very Large Array (VLA) in New Mexico is one of the largest interferometers. It is sometimes linked with other arrays of telescopes outside the US, or even in space, to mimic an even larger configuration.

Electromagnetic radiation with wavelengths between those of radio waves and visible light is called infrared light. We encounter it in our daily lives for example in heat lamps and night-vision cameras. Infrared telescopes have also been very important for astronomy, for example to study star formation. The Spitzer Space Telescope, which orbits around the Earth, is one of the most powerful infrared telescopes."/*&*/ /*&*/image16="radio"/*&*/ /*&*/caption16_visible="The VLA in the desert of New Mexico has 27 radio antennas that can be moved along railroad tracks over 22 miles."/*&*/ /*&*/caption16_radio="The Arecibo radio telescope in Puerto Rico is built into a natural valley. Grasp the scale by looking at the cars in the foreground."/*&*/ /*&*/caption16_xray="Arist impression of the Spitzer Space Telescope, which can image and analyze infrared light from objects in the Universe."/*&*/ /*&*/link_url16_1="http://en.wikipedia.org/wiki/Radio_astronomy"/*&*/ /*&*/link_url16_2="http://www.vla.nrao.edu/"/*&*/ /*&*/link_url16_3="http://coolcosmos.ipac.caltech.edu/"/*&*/ /*&*/link_url16_4="http://www.allthesky.com/articles/imagecolor.html"/*&*/ /*&*/link_displayed16_1="More facts about radio astronomy"/*&*/ /*&*/link_displayed16_2="The Very Large Array"/*&*/ /*&*/link_displayed16_3="Learn about the infrared universe"/*&*/ /*&*/link_displayed16_4="True and false colors in astronomical images"/*&*/ /*&*/observatoryName17="What instruments do astronomers use to find black holes?"/*&*/ /*&*/maintext17="When our eyes look at the heavens we see the visible light from stars and other objects in the Universe. Thousands of years ago astronomers in Greece and other ancient cultures already built a detailed understanding of the night sky. Many names and concepts then developed are still in use today. However, our human eyes are actually not very sensitive and modern astronomers use sophisticated telescopes to study the Universe.

The telescopes used by astronomers do not just study visible light. While visible light is the type of 'electromagnetic radiation' that our eyes can see, there are many other types of such radiation. Different types of radiation are characterized by different wavelengths. If the wavelength is much shorter than that of visible light we speak about X-rays. We encounter X-rays often in our daily lives, for example at the hospital or during security screening. If the wavelength is much larger than that of visible light we speak about radio waves. We encounter radio waves often in our daily lives, for example in radios and cell phones.

The black holes in the Universe do not emit any detectable type of light. However, astronomers can still find them and learn a lot about them. They do this by measuring the visible light, X-rays and radio waves emitted by material in the immediate environment of a black hole. For example, when a normal star orbits around a black hole we can measure the speed of the star by studying the visible light that it emits. Knowledge of this speed can be combined with the laws of gravity to prove that the star is in fact orbiting a black hole, instead of something else. It also yields the mass of the black hole. Alternatively, when gas orbits around a black hole it tends to get very hot because of friction. It then starts emitting X-rays and radio waves. So black holes can also often be found and studied by looking for bright sources of X-rays and radio waves in the sky.

There are many other types of electromagnetic radiation as well. Radiation that has even smaller wavelengths (and even higher energies) than X-rays is called gamma-rays. Radiation with wavelengths between those of X-rays and visible light is called ultraviolet light. We encounter ultraviolet light in our daily lives for example in fluorescent lamps. Ultraviolet telescopes allow astronomers to study things such as the composition of the gas that exists between stars. Electromagnetic radiation with wavelengths between those of radio waves and visible light is called infrared light. We encounter infrared light in our daily lives for example in heat lamps and night-vision cameras. Infrared telescopes allow astronomers to study things such the formation of stars.

The following links provide more information about the types of radiation that are most important for studies of black holes, and about the telescopes that astronomers use to study them:"/*&*/ /*&*/image17="TBD"/*&*/ /*&*/caption17_visible="Artist impression of the GALEX satellite, which can make images of the ultraviolet light from astronomical objects."/*&*/ /*&*/caption17_radio="Artist impression of the Spitzer Space Telescope, which can image and analyze infrared light from objects in the Universe."/*&*/ /*&*/caption17_xray="none"/*&*/ /*&*/link_url17_1="http://imagine.gsfc.nasa.gov/docs/introduction/gamma_information.html"/*&*/ /*&*/link_url17_2="http://www.galex.caltech.edu/"/*&*/ /*&*/link_url17_3="http://fuse.pha.jhu.edu/outreach/"/*&*/ /*&*/link_url17_4="http://coolcosmos.ipac.caltech.edu/"/*&*/ /*&*/link_displayed17_1="Learn about gamma-ray astronomy"/*&*/ /*&*/link_displayed17_2="The Galaxy Evolution Explorer (GALEX)"/*&*/ /*&*/link_displayed17_3="The Far Ultraviolet Spectroscopic Explorer"/*&*/ /*&*/link_displayed17_4="Learn about the infrared universe"/*&*/ /*&*/observatoryName18="Visible Light"/*&*/ /*&*/maintext18="The first visible light telescope, invented 400 years ago, used an arrangement of lenses and was small enough to hold by hand. Modern telescopes are much larger, so that more light can be caught and fainter objects can be seen. Curved mirrors are used to focus the light and record it on sophisticated electronic equipment. The 5 meter (200 inch) Hale telescope on California's Palomar Mountain, completed in 1948, was the largest telescope for several decades. This honor is now held by the two Keck telescopes on Mauna Kea in Hawaii, each with a mirror diameter of 10 meters.

To minimize image blurring due to the Earth's atmosphere, telescopes are usually built on high mountains. Mirror deformation technologies now also exist to correct for atmospheric blurring. But even better results are achieved with a telescope in orbit above the Earth atmosphere, such as the Hubble Space Telescope. It has a 2.4 meter diameter mirror in a satellite the size of a school bus. It has produced some of the sharpest and most stunning images ever obtained, has found supermassive black holes in many galaxies, and continues to revolutionize our understanding of the Universe."/*&*/ /*&*/image18="visible"/*&*/ /*&*/caption18_visible="The Hubble Space Telescope flies around the Earth and provides stunning images from high above the atmosphere."/*&*/ /*&*/caption18_radio="The Palomar Hale 5 meter telescope inside its dome (inset on left). Grasp the scale by looking at the ladder below the telescope."/*&*/ /*&*/caption18_xray="The 10 meter Keck telescopes on Hawaii's Mauna Kea mountain. Grasp the scale by looking at the cars in front of the building."/*&*/ /*&*/link_url18_1="http://en.wikipedia.org/wiki/Telescope"/*&*/ /*&*/link_url18_2="http://www.astro.caltech.edu/observatories"/*&*/ /*&*/link_url18_3="http://hubblesite.org/"/*&*/ /*&*/link_url18_4="http://skyandtelescope.com/howto/basics/article_260_1.asp"/*&*/ /*&*/link_displayed18_1="More facts about telescopes"/*&*/ /*&*/link_displayed18_2="Palomar | Keck Observatories"/*&*/ /*&*/link_displayed18_3="Hubble Space Telescope"/*&*/ /*&*/link_displayed18_4="How to make stargazing your hobby"/*&*/ /*&*/observatoryName19="X-rays"/*&*/ /*&*/maintext19="X-rays have much higher energy than visible light and cannot pass through the Earth atmosphere. So one must launch a special kind of telescope above the atmosphere to see X-rays from astronomical objects. The first X-ray telescopes in the 1960s led to many important discoveries (as recognized by the 2002 Nobel Prize in Physics). X-ray astronomy is now routinely used to provide insight into some of the most energetic processes in the Universe, including the swallowing of matter by black holes. The most powerful X-ray telescopes that currently orbit the Earth are the Chandra X-ray Observatory and XMM Newton telescope."/*&*/ /*&*/image19="xray"/*&*/ /*&*/caption19_visible="Artist impression of the Chandra X-ray Observatory. It can take sharper X-ray images than any other telescope."/*&*/ /*&*/caption19_radio="Artist impression of the XMM Newton X-ray Observatory. It can detect fainter X-ray signals then any other telescope."/*&*/ /*&*/caption19_xray="none"/*&*/ /*&*/link_url19_1="http://imagine.gsfc.nasa.gov/docs/introduction/xray_information.html"/*&*/ /*&*/link_url19_2="http://chandra.harvard.edu/"/*&*/ /*&*/link_url19_3="http://xmm.sonoma.edu/index.html"/*&*/ /*&*/link_url19_4="none"/*&*/ /*&*/link_displayed19_1="More facts about X-ray astronomy"/*&*/ /*&*/link_displayed19_2="The Chandra X-ray Observatory"/*&*/ /*&*/link_displayed19_3="The XMM-Newton X-ray telescope"/*&*/ /*&*/link_displayed19_4="none"/*&*/ /*&*/observatoryName20="Radio Waves"/*&*/ /*&*/maintext20="In the mid 1900s it was discovered that many objects in the Universe shine in radio waves. This led to the development of radio telescopes, which are special antennas for detecting and imaging the radio signals from astronomical objects. Radio telescopes have yielded new insights into many aspects of the Universe, including black holes and cool gas. The largest single-dish radio telescope is the Arecibo Telescope in Puerto Rico. With a radio interferometer astronomers create very sharp images by combining the signals from many individual radio dishes spread over a large area. The Very Large Array (VLA) in New Mexico is one of the largest interferometers. It is sometimes linked with other arrays of telescopes outside the US, or even in space, to mimic an even larger configuration."/*&*/ /*&*/image20="radio"/*&*/ /*&*/caption20_visible="The VLA in the desert of New Mexico has 27 radio antennas that can be moved along railroad tracks over 22 miles."/*&*/ /*&*/caption20_radio="The Arecibo radio telescope in Puerto Rico is built into a natural valley. Grasp the scale by looking at the cars in the foreground."/*&*/ /*&*/caption20_xray="none"/*&*/ /*&*/link_url20_1="http://en.wikipedia.org/wiki/Radio_astronomy"/*&*/ /*&*/link_url20_2="http://www.vla.nrao.edu/"/*&*/ /*&*/link_url20_3="http://www.vsop.isas.jaxa.jp/"/*&*/ /*&*/link_url20_4="http://www.allthesky.com/articles/imagecolor.html"/*&*/ /*&*/link_displayed20_1="More facts about radio astronomy"/*&*/ /*&*/link_displayed20_2="The Very Large Array"/*&*/ /*&*/link_displayed20_3="Radio telescope in space"/*&*/ /*&*/link_displayed20_4="True and false colors in astronomical images"/*&*/